Liquid crystal displays (LCDs) are commonly used in various electronics, such as cell phones, laptops, electronic tablets, televisions, and computer monitors. However, LCDs can be limited as compared to other display devices in terms of brightness, contrast ratio, efficiency, and viewing angle. For instance, to compete with organic light emitting diode (OLED) technology, there is a demand for higher contrast ratio, color gamut, and brightness in conventional LCDs while also balancing power requirements, e.g., in the case of handheld devices. Further, an emerging trend in electronics includes transparent displays which allow the user to the see device components or other objects behind the display panel. However, existing backlight technology may, at best, provide a distorted view of the objects behind the panel or may partially or completely block view of these objects. Finally, overall consumer demand for thinner LCD devices drives the need for thinner backlight stacks.
Conventional LCD backlights may include a light guide comprising polymethyl methacrylate (PMMA). However, attempts to make thinner backlight stacks using thinner sheets of PMMA may have drawbacks of high price and/or low strength (flimsiness). Moreover, the thickness of conventional LCD backlights may also be affected by the presence of various polymer films, which serve to transport the light from the backlight to the backplane of the liquid crystal. For instance, the light may be injected into a transparent, e.g., PMMA, light guide with light extraction features that emit the light at large angles (e.g., greater than about 70 degrees). Light emitted toward the display may hit brightness enhancing films that alter its direction so that more light is emitted normal to the screen. Light emitted towards the LCD panel with polarization perpendicular to the polarizer in the LCD backplane may then hit a film that selectively reflects that polarization back through the backlight stack to reflect off of a Lambertian scattering layer of the reflector with a randomized polarization. The Lambertian scattering layer behind the light guide may reflect the recirculated light and the light emitted away from the LCD by the light guide back towards the LCD panel. The thickness of the backlight stack increases with the addition of each layer and may inhibit the ability to create thinner LCD devices. Moreover, the presence of additional layers may decrease the brightness of the device display, as each layer may transmit only a portion of the light incident on it.
Patterned backlights have been explored as a potential remedy to one or more of the drawbacks above but to Applicants' knowledge are not presently commercialized. For instance, U.S. Pat. No. 6,791,636, incorporated herein by reference in its entirety, is directed to patterned light guides. However, the alignment tolerance required between the three-dimensional light extraction features on a patterned light guide and the LCD thin-film transistor (TFT) is very tight, thus limiting the use of such patterned light guides in commercial applications.
Accordingly, it would be advantageous to provide backlights for LCD devices which address one or more of the above drawbacks, e.g., thinner backlights with lower cost and/or higher strength, backlights that require fewer layers for transporting light, and/or backlights with improved alignment stability between the light guide and the TFT. In various embodiments, LCD devices comprising such backlights may be brighter, may have a higher contrast ratio, may have improved viewing angles, and/or may be more energy efficient.